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NOVEMBER 2022
The faecal glove sedimentation test is popular in practice
but the authors caution that extreme care should be exercised in its interpretation as many horses on sandy pasture will pass sand in their faeces which may simply represent ingestion (Filgueiras et al., 2009). Multiple variations of the faecal sedimentation (glove) test have been described (Colahan, 1987; Husted et al., 2005) but, in principle the test involves mixing faeces and water and letting the sand sediment to the fingertips of a disposable glove or the bottom of a bag. In one study of patients radiographed due to a clinical suspicion of sand enteropathy, the faecal glove sedimentation test had a sensitivity, specificity, positive predictive value and negative predictive value of 83%, 71%, 90% and 56%, respectively, when it was compared with radiography (Hukkinen, 2015). However, it warrants note that 29% of horses in the study had received treatment prior to the faecal sample collection, an intervention which is likely to have artificially elevated the sensitivity of the test. Further, the prevalence of sand accumulations in that study was high (65%) as it reflected a population with a high clinical index of suspicion. Considering this, where the pretest probability is high, such as in a patient with appropriate clinical signs, the positive predictive value of the faecal glove sedimentation test is such that a positive test may be adequate to justify treatment; however, a negative test cannot be used to rule out disease. In contrast, where the pretest probability is low, such as
when the test is used as a screening test in a population exposed to sand, the test performs poorly. Horses on sandy pastures commonly excrete sand in their faeces without any signs of problems related to sand enteropathy. In one study, where horses were kept on a sandy pasture, all horses (112/ 112) excreted some sand in their faeces, although none had clinical signs related to gastrointestinal disease (Filgueiras et al., 2009). In another study screening horses in a free range, naturally sandy environment 85% and 23% of horse had >0.5 mm and >5 mm of sand in a fingertip of the glove, respectively (Reichelt & Lischer, 2001). In that study, that had a prevalence of 25% for moderate-severe sand accumulation identified radiographically, the sensitivity, specificity, positive predictive value and negative predictive value of the faecal glove sedimentation test (defined as >5 mm of sand in a fingertip of the glove) were 27%, 80%, 31% and 77%, respectively (Reichelt & Lischer, 2001). Considering these studies, the authors’ opinion is that the test lacks diagnostic accuracy under these conditions, and it should not be used as a screening test in animals without clinical signs within at-risk populations. Ultrasound is an alternative means of diagnosis which has
been reported to have sensitivity and specificity both of 87.5% when compared with radiography (Korolainen & Ruohoniemi, 2002). The technique is performed along the ventral abdomen and sand accumulations in the large colon appear hyperechoic with acoustic shadowing (Korolainen & Ruohoniemi, 2002). When applied as a screening test, using a pretest probability of 25% in a population exposed to sand but without clinical signs (Reichelt & Lischer, 2001), the positive and negative predictive values of ultrasound are 70% and 95%, respectively. Under these conditions, the high negative predictive value makes ultrasound a useful screening test for ruling out sand accumulation, but the relatively low positive predictive value should be considered in the event of a positive test. In contrast, in a recent study of
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22 colic horses that had radiographically confirmed sand accumulations none had sand detected ultrasonographically (Graubner et al., 2017). This suggests that the utility of ultrasound for diagnosis of sand accumulation in the acute setting is, at best, limited. However, ultrasound is likely to be useful in suspected cases of sand impactions to identify pockets of abdominal fluid and to avoid accidental enterocentesis. Radiography is considered the reference standard for
diagnosis of sand enteropathy, as sand and other types of geosediment give a distinct shadow of mineral opacity in the abdominal radiograph (Fig 1a and b). Absolute size, or size relative to the horse’s size, has been used to categorise sand accumulations in order to compare these with clinical signs or the accuracy of other diagnostic methods (Kaikkonen et al., 2000, 2016; Ruohoniemi et al., 2001; Korolainen & Ruohoniemi, 2002; Kendall et al., 2008; Keppie et al., 2008; Hart et al., 2013; Kilcoyne et al., 2017, Niinist€
systems based on height and length (Kendall et al., 2008; Korolainen & Ruohoniemi, 2002) or area (Kaikkonen et al., 2016; Kilcoyne et al., 2017; Niinist€
o et al., 2014, 2018) of the
accumulation visible in the radiograph have been used to describe the two-dimensional size of the accumulation. The exact amount of radiographically measured sand required to cause disease is not known but >75 cm2 has been suggested as clinically relevant breakpoint (Korolainen & Ruohoniemi, 2002; Niinist€
o et al., 2019). Occasionally diagnosis may be made during other
examinations of a horse with acute colic and both rectal palpation of sand, and abdominocentesis with iatrogenic enterocentesis of the sand-filled colon have been reported (Ferraro, 1973; Ford & Lokai, 1979; Udenberg, 1979; Colahan, 1987; Specht & Colahan, 1988; Ragle et al., 1989a; Hart et al., 2013; Kilcoyne et al., 2017). Occasionally sand can be palpated in the faeces or in part of the gastrointestinal tract such as the pelvic flexure (Ferraro, 1973; Ford & Lokai, 1979; Colahan, 1987; Ragle et al., 1989a; Hart et al., 2013). There are no reports regarding changes in peritoneal fluid that would be specific for sand accumulation, and abdominocentesis findings are most likely reflective of bowel viability and inflammation (Hart et al., 2013; Kilcoyne et al., 2017). Similar to peritoneal fluid, there are no haematological or serological changes speficit for sand enteropathy (Niinist€ et al., 2014).
o
Treatment The mainstays of medical treatment of acute colic, including colic associated with sand accumulation, are to control pain, increase hydration of intestinal contents and promote gastrointestinal motility. This is achieved with fluid therapy, analgesics, cathartics and withholding feed until any associated impaction is resolved (Rakestraw & Hardy, 2012). Once the acute crisis has been resolved, the focus of treatment then shifts to removal of the sand accumulation. The use of psyllium for the treatment of sand enteropathy
is a long standing practice (Ferraro, 1973) although, until recently, little evidence has existed to support its use in clinical patients with experimental studies demonstrating no effect (Hammock et al., 1998) or only modest effects (Hotwagner & Iben, 2008; Landes et al., 2008) of psyllium on clearance of sand accumulations or faecal sand output. Magnesium sulphate is a commonly used laxative for large
o et al., 2019). Grading
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